As said in contest conditions, you can use any 3D model you want, private or publicly available, as long as we can publish an image of it on Sweet Home 3D web site. If you're the author of that model I guess you won't mind to show it to others.
A problem may arise if I want to publish the SH3D file of your project at the end of the contest, because publishing such a file is some kind of redistribution of the 3D models it includes. If your SH3D file uses some models that you're not allowed to redistribute, I won't be able to publish your SH3D file. But you can still submit your image, since it's a photo contest not a SH3D file contest.
I hope it's clearer...
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Emmanuel Puybaret, Sweet Home 3D creator
